Plastic encapsulated semiconductor devices are susceptible to moisture ingress due to the permeable nature of plastic molding compounds. The amount of moisture that a plastic resin encapsulated semiconductor device absorbs from its environment is dependent on several factors: the length of exposure time to the environment, the diffusivity of the plastic or how quickly moisture can be absorbed into the material, the solubility coefficient of the plastic or its saturation capacity, and the thickness of the plastic body on the device. Devices containing moisture levels exceeding some critical amount run the risk of cracking or "popcorning" during the rapid heating of the solder reflow operation associated with board mounting of devices. Semiconductor devices which are subject to cracking are normally baked in an oven at approximately 125.degree. C., a typical temperature, for a predetermined length of time to drive moisture out of the devices before they are shipped to the customer. Those devices that are deemed to be moisture sensitive are packaged in "dry-packs" after baking to ensure that they are protected from moisture thereafter and will arrive dry at the customer site. Otherwise, devices that have absorbed a certain level of moisture run the risk of cracking during the solder reflow operation. Mechanical failure of the semiconductor devices often times lead to subsequent electrical failure of these same devices due to thermal and mechanical stresses induced on the devices during their operation.
Current dry-packing practices involve baking semiconductor devices until dry, placing them into a dry-pack bag with desiccant packets and a humidity indicator card, vacuum sealing the bag immediately thereafter, and shipping the devices to the customer in these dry-packs. The vacuum seal is a highly important component of the dry-pack process because the seal prevents moisture ingress into the dry-pack bag. The dry-pack bag is typically made from a flexible plastic material. A problem with the current method of dry-packing is that once the bag is sealed, determining the integrity of the vacuum seal thereafter is difficult. A reason for this difficulty is that the trays used in shipping semiconductor devices can sometime fit tightly into the dry-pack bag, making the bag taut. Thus, it becomes difficult to quickly determine whether the vacuum seal is still intact or not because the dry-pack bag is not loose. Sometimes, the leak can be as small as a pinhole which makes it difficult to detect. The humidity indicator card is limited to only indicating the present level of moisture to which the card, and thus its surroundings, has been exposed. The humidity indicator card does not provide any indication of the seal condition of the dry-pack bag.